Global Gene Expression Associated with Hepatocarcinogenesis in Adult Male Mice Induced by in Utero Arsenic Exposure

Abstract

Our previous work has shown that exposure to inorganic arsenic in utero produces hepatocellular carcinoma (HCC) in adult male mice. To explore further the molecular mechanisms of transplacental arsenic hepatocarcinogenesis, we conducted a second arsenic transplacental carcinogenesis study and used a genomewide microarray to profile arsenic-induced aberrant gene expression more extensively. Briefly, pregnant C3H mice were given drinking water containing 85 ppm arsenic as sodium arsenite or unaltered water from days 8 to 18 of gestation. The incidence of HCC in adult male offspring was increased 4-fold and tumor multiplicity 3-fold after transplacental arsenic exposure. Samples of normal liver and liver tumors were taken at autopsy for genomic analysis. Arsenic exposure in utero resulted in significant alterations (p < 0.001) in the expression of 2,010 genes in arsenic-exposed liver samples and in the expression of 2,540 genes in arsenic-induced HCC. Ingenuity Pathway Analysis revealed that significant alterations in gene expression occurred in a number of biological networks, and Myc plays a critical role in one of the primary networks. Real-time reverse transcriptase–polymerase chain reaction and Western blot analysis of selected genes/proteins showed > 90% concordance. Arsenic-altered gene expression included activation of oncogenes and HCC biomarkers, and increased expression of cell proliferation–related genes, stress proteins, and insulin-like growth factors and genes involved in cell–cell communications. Liver feminization was evidenced by increased expression of estrogen-linked genes and altered expression of genes that encode gender-related metabolic enzymes. These novel findings are in agreement with the biology and histology of arsenic-induced HCC, thereby indicating that multiple genetic events are associated with transplacental arsenic hepatocarcinogenesis.

Aberrant DNA methylation and gene expression in livers of newborn mice transplacentally exposed to a hepatocarcinogenic dose of inorganic arsenic

“…The increased expression of the female-predominant CYP2A4 in newborn liver is consistent with our prior observations in arsenic transplacental carcinogenesis studies in adult liver (Waalkes et al, 2004b;Liu et al, 2006) as well as in fetal liver . CYP2A4 encodes for hepatic microsomal androstenedione 15α-hydroxylase and its overexpression would imply altered steroid metabolism.…”

“…The expression of HSD17β5 dehydrogenase, an enzyme catalyzing the transformation of 4-androstenedione (4-dione) into testosterone, was also decreased. These changes are consistent with male liver feminization and a role of aberrant estrogen signaling seen in our series of transplacental arsenic carcinogenesis studies (Waalkes et al, 2004b(Waalkes et al, , 2006aLiu et al, 2006Shen et al, 2007).…”

“…Glutathione (GSH) systems play important roles in arsenic toxicity, adaptation, and perhaps carcinogenesis (NRC, 2001;Xie et al, 2004;Liu et al, 2006). In the present study, the expression of glutathione S-transferase mu (GST-mu), GST-pi, GST-alpha and GST-theta were all increased by in utero arsenic exposure in newborn mouse liver.…”

Arsenic in drinking water causes gene expression changes in the liver related to inflammation and metabolic dysfunction and accelerates atherosclerosis in ApoE-/-mice

“…In general, microRNA pointed to broad functions such as biological regulation, transcription regulatory activity, and blood vessel morphogenesis that support their supposed functions. Gene alterations seen in the present study are largely consistent with previous analyses in gene expression on arsenic in drinking water [33,36,[43][44][45]52]. Below is a critical discussion of the information contained in the results.…”

“…Arsenic is metabolized in the liver by humans and rodents, and the liver is a known target of arsenic toxicity causing abnormalities such as fibrosis and hepatocarcinoma The Waalkes lab has published articles elucidating mechanisms of arsenic-induced liver injury [36,45] including a literature review [38]. Among potential mechanisms for arsenic hepatocarcinogenesis are oxidative damage and stress, altered DNA repair, protein interaction with zinc finger proteins, hypo-and hypermethylation, and aberrant estrogen linked gene expression.…”